Known in the art is a coordinate grid for a stereoscopic measuring device (SU, A, 147779) in the form of a support carrying a plurality of sterephotographs disposed in a succession and representing images of scales each in the form of a system of mutually perpendicular crossing straight lines. Each stereophotograph of this plutality of stereophotographs is made with a parallax and in a scale corresponding to a single specific range to the camera exposure station, i.e. to a distance from the camera exposure station to a single specific plane in the object space drawn normally with respect to the optical line of exposure.
A stereophotograph of an object is measured using the prior art coordinate grid in the following manner.
A film with a stereophotograph of an object (photograph to be measured) is mounted in a stereoscopic measuring device and is optically aligned with one of the measuring scales available on the support inserted in the device and carrying a plurality of stereophotographs with scale images. With the known measurement scale division, the range and dimensions of an object shown in the photograph are determined in that part thereof which corresponds to the specified range for a given scale. To determine the range and dimensions of objects available in other parts of the photograph, the support carrying stereophotographs of scales is moved with respect to the photograph to choose that scale which cann be visually brought in register with the object on the measured part of the photograph, and the actual dimensions and position of the object are determined in coordinates of this scale. In other words, in using the prior art coordinate grid, each change scale allows measurements to be carried out in a single specific plane of the object space only which is drawn normally with respect to the optical line. The prior art coordinate grid does not fill-up the photograph field in depth in the direction along the optical line of exposure. Measurements carried out by using the prior art coordinate grid are tedious and take much time. In addition, accuracy of measurements is limited by the discrete character of the series of design ranges of scales, and it is not possible to isolate objects for measurements within the space, e.g. density of biomass.
Also known in the art is a coordinate grid for a stereoscopic measuring device (DE, C, 3341087) in the form of a support carrying a stereophotograph of images of at least one group of straight lines converging at one and the same point and closed lines interconnecting them, the grid having divisions. The closed lines form contours of rectangles, i.e. the grid is in the form of intersection of straight lines, and its stereoscopic model is in the form of a three-dimensions rectilinear pattern with known nodal coordinates under binocular observation. When a stereoscopic image of an object is measured by means of this grid, dimensions of parts of the object can be determined simultaneously with different ranges thereto. Volumes for measurement, e.g. density of biomass may be isolated in the space as well. At the same time, accuracy of measurement which can be ensured using this grid depends on its spacing. With an increase in density of the grid accuracy of measurement is enhanced, but this also brings about the formation of phantom images in using the grid formed by straight lines (a similar phenomenon is known in the stereophotogrammetry as formation of a phantom relief) so as to limit accuracy of measurements. It should be also noted that in using grids formed by straight lines it is difficult to make corrections to grid dimensions to take into account distortion, especially in carrying out the exposure with short-focus lenses or in water which also results in a worse accuracy, especially in carrying out measurements in the marginal zones of the photograph.